Destruction of Coral
Coral reefs are one of the most precious living structures that the Earth is endowed
with, because they provide protection for coastal areas from the rough oceans. They
prevent erosion by creating a buffer against the constant wave action of the ocean. Corals
also create a safe haven for young tropical fish by providing small niches for them to hide
in and to get away from large predators. Unfortunately in today’s busy society, people
who are not directly involved with corals do not understand the role that human behaviors
and actions play in the destruction of coral reefs.
Global warming is a popular topic in today’s society. Climate change is also believed
to play an important role in altering. To be specific it is interrupting the natural cycles of
the ocean. Due to the amount of fossil fuels that are being used, the ocean is slowly being
acidified. Acid rain and acid run-off are a by-product of global warming. Ocean
acidification is the process by which seawater dissolves carbon dioxide from the
atmosphere. This dissolution subsequently causes the pH level to decrease in the ocean.
In turn the coral’s ability to produce calcium carbonate will decrease thus lowering the
density of the calcium skeleton. Acidification also damages corals by decreasing the rate
at which they grow, a condition also referred to as stunted growth. The corals’ skeletons
will be weaker, thus exposing them to a greater level of predation. Corals are one of the
oldest living organisms on the Earth and do not have the capacity to quickly adapt to
changes in their microclimate. If the microclimate continues to experience dramatic
shifts, corals will soon become extinct.
Another harmful effect that global warming has on coral is bleaching. Bleaching is the
most common and destructive agent that kills coral. Corals are very vulnerable to
changing temperatures and salinity levels, thus other types of stressors can easily affect
them. The symbiotic algae, zooxanthalle, that corals are bonded to are then expelled from
the coral resulting in coral starvation. Bleaching is caused by ocean acidification. When
bleaching occurs the zooxanthalle detach from the polyps. The polyp is then vulnerable
(disease, predation etc.); it unable to grow, becomes weaker and thus more susceptible to
diseases. The zooxanthalle are what give corals their brilliant colors, thus when they are
expelled the corals become colorless. All of these destructive elements stress the coral
causing eventual death.
The continuous rise in ocean temperatures over the last 50 years has directly affected
coral. Due to the increasing temperatures harmful algae and bacteria have started to grow
in the same environment. Algal blooms blacken out the much-needed sunlight that allows
photosynthesis to occur within the coral’s structure. In addition, bacteria thrive in the
warmer temperatures and can harm the already weakened coral. Black band disease is
caused by cyanobacteria. When coral is infected with this bacterium it quickly consumes
the polyps of coral by separating the living polyps from their skeleton. It can spread at a
rate as fast as 1cm per a day. After infection the only remainder that black band disease
leaves is the bare skeleton of the coral. Scientists are still trying to discover how the black
band disease spreads, as well as identifying its origin.
Violent ocean storms are more prevalent today, often producing devastating wave
action in their wake. Tsunamis and hurricanes are particularly threatening as their storm
surges easily break coral reef systems. If the coral is not strongly attached to the sediment
they can easily be washed away by the strong wave action. It cannot kill a coral reef
completely, but it can damage it to quite an extent. If they are resilient some reefs are
able to recover, but it takes an average of 20 years or more to recover from a violent
storm. If corals are already weakened by predation, diseases, or other factors the chances
of them surviving a storm is greatly reduced.
In many foreign countries, such as the Philippines, the locals or artisanal fisherman
catch fish by using explosives. Many of the Asian countries collect large numbers of
specific reef fish and ruin the ecosystem of the reef by continually hunting the largest
predator and thus breaking the food chain. It is not just the locals that are at fault, but
also divers. Rather than catching the fish one by one, they use explosives so that they can
collect as many as possible. These explosives while releasing toxic chemicals into the
water in order to stun fish are also breaking apart coral reef systems. The explosion
causes devastation to the reef in many ways. The coral is shattered into pieces and the
fish that were living there have to find new homes. Another major chemical that is spilt
into the ocean is cyanide. Cyanide stuns or kills the fish and in this process also kills the
corals by poisoning the coral reef.
It is not just the chemicals that the fishermen use that adversely affects corals, but
also those applied to fields by farmers. Runoff from fertilizers, insecticides and
pesticides, which are used to increase crop yields, has a deleterious effect on coral. The
main reason is due to the increase in the amount of nitrogen and phosphate deposited into
the water, which in turn increases the level of algal blooming. Corals cannot afford to
compete with the algae for sunlight. Algae will win because it reproduces at a much
faster rate than coral. In addition the large amount of algal waste product produces toxic
levels of phosphorous and nitrates which then accumulate in the corals’ environment.
After a while the reproduction of algae will use up all of the available resources that
corals need because it eventually removes all the oxygen from the water. The prolific
spread of algae will eventually create an anoxic environment for the corals, further
stressing the already vulnerable creatures.
Crown of thorns, a type of sea star, eats coral polyps. They climb over the coral,
stretching themselves out, and then eject their stomachs. (See Figure 1) The gastric juices
dissolve the polyps and leave behind the stony skeleton. Recently the crown of thorns
have become highly invasive. Large groups of these sea stars are referred to as
aggregations. The reason why scientists are concerned about the rapid increase in their
population is because they are affecting one of the largest reefs in the world, the Great
Barrier Reef. Every couple of years these organism reproduce in large numbers causing
devastation to coral, but scientists have figured out a way to predict and try to lessen the
devastating effects of these outbreaks. Unfortunately these breakouts can lead to large
areas of deceased corals.
Parrotfish and butterfly fish both eat algae found growing on coral, but in the process
also damage the reef. Parrotfish have large teeth for chopping and manage to reduce hard
coral skeletons to fine grains of sand. While they are clearing the coral of the hanging
algae they are also breaking little bits of coral off. Butterfly fish and parrotfish compete
for the algae growing on coral reefs, but each have developed tactics to avoid each other
and protect themselves. Drupella snails are also predators of corals. They are miniscule
yet can cause much damage to the structure of corals. They have the same effect as the
crown of thorns. An abundance of snails can reek havoc on coral reefs. A white scar is
the evidence that indicates that the Drupella snail has recently fed on corals.
Figure 1: ( Library Thinkquest) Juvenile Crown of Thorns feeding on coral
ANTHROPOGENIC ( HUMAN ACTIVITY)
Anthropogenic activities are also damaging to coral reefs mainly due to the
overexploitation of resources that the reefs provide. Fishermen hunt many of the larger
fish and interrupt the food web. Once there are no longer large predators, the smaller fish
become more abundant and increase predators’ behavior on the level below them. People
illegally remove and transport rare fish to black markets to be sold at high prices. By
removing and transporting these creatures from their natural habitat it can kill them and
decrease natural populations to even lower levels. Coral is also collected to be used as
jewelry. Ripping these pieces off the reef damages it as a whole and encourages people to
buy it. In many stores, tourists have the opportunity to bring a piece of their trip back
with them, coral. By buying these rare animals from stores it encourages natives to go
and collect more.
Many countries depend on tourism to stimulate their economy. Many who go to
observe coral reefs are guilty of damaging corals. Scuba divers who go to enjoy reefs are
some of the major offenders. Their equipment can drag along the bottom and remove
coral from the sediment that it has settled on. Inexperienced divers who have problems
with buoyancy control can injure corals as well. Underwater photographers also can
damage corals by getting too close or kneeling on it in order to get a closer picture.
Irresponsible boaters that go out onto the reefs to observe, fish and enjoy the reefs can
ruin them by dropping their anchors into the reef system, itself.
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